To improve fuel economy, hybrid electric vehicles (HEVs) may provide regenerative (regen) braking, in which kinetic energy is converted by an electric machine into storable energy during braking and then made available for propulsion. In many HEVs, the regen components collect energy from one axle only such that when braking is required, the regen energy is collected first up to the regen or traction/stability limit, followed by application of friction brakes at the other axle or both axles to slow or stop the vehicle. During regenerative braking, collection of regen energy from one axle only may not balance brake torque between the front and rear wheels in proportion to available traction at each wheel, which could affect vehicle stability.
Therefore, a regenerative brake control system and method for four-wheel drive vehicles which optimizes apportionment of regenerative brake torque to all four wheels of a vehicle while maintaining vehicle stability is needed.